Update docs to always use yarn add --cwd for app & backend

Some commands currently error, and others are simply formatted inconsistently.
This format seems to work and be the most popular/common,
so I applied it to all similar occurrences.

Signed-off-by: Jan Van Bruggen <JanVB@verily.com>

plugins/azure-devops-backend/README.md

@@ -30,9 +30,8 @@ Here's how to get the backend up and running:
 1. First we need to add the `@backstage/plugin-azure-devops-backend` package to your backend:
 
    ```sh
-   # From the Backstage root directory
-   cd packages/backend
-   yarn add @backstage/plugin-azure-devops-backend
+   # From your Backstage root directory
+   yarn add --cwd packages/backend @backstage/plugin-azure-devops-backend
    ```
 
 2. Then we will create a new file named `packages/backend/src/plugins/azure-devops.ts`, and add the